This invention relates to thickener compositions for water-based hydraulic fluid compositions and metalworking fluid or lubricant compositions, which are thickened to an oil-like viscosity by the interaction of thickeners at a low solids concentration. More particularly, this invention relates to thickener compositions, hydraulic fluid and metalworking fluid concentrates, aqueous concentrates and water-based hydraulic fluid and metalworking lubricant compositions employing polyurethanes and dimer esters.
In hydraulic machinery, mechanical force is imparted to a fluid, known as hydraulic fluid, in the form of pressure by means of a hydraulic pump. The energy imparted to the hydraulic fluid is utilized by transforming this pressure energy back to mechanical energy by a hydraulic motor mechanism. In this manner, the hydraulic fluid is utilized as a pressure and volume transmitting medium. Therefore, the main function of a hydraulic fluid is power transfer.
According to U.S. Pat. No. 4,312,768, any non-compressible fluid can perform the function of a hydraulic fluid, including water. However, heavy emphasis has been placed on the development of petroleum oils for use as hydraulic fluids. Petroleum-based hydraulic fluids are said to offer several advantages over water-based hydraulic fluids. First, water-based fluids are said to suffer from the development of rust of the ferrous components of the mechanical equipment. Second, oil-based products have been reported to prevent the wear of machinery by lubricating the equipment. Third, oil-based products are believed to exhibit greater viscosity than water-based ones and thus account for the reduction of fluid leakage in the mechanical equipment utilized. Finally, the development of technology for fluid additives has advanced to such an extent that improvement in viscosity, foam stability, wear prevention and corrosion prevention properties is further enhanced by the use of such additives in oil-based hydraulic fluids.
However, even with the reported advantages of oil-based fluids, they continue to suffer from such deficiencies as flammability, higher costs, environmental pollution and/or disposal problems.
Additional important characteristics that a hydraulic fluid should possess include pump volume efficiency, which is closely related to its rheological properties, and good wear resistance. Low wear rates increase the pump life of a hydraulic fluid. Additionally, compositions which are stable throughout a temperature range not only maintain their viscosity, but also their chemical integrity.
Metalworking fluid compositions should also function to reduce friction and heat generation, hence to provide lubrication and cooling in the cutting area in order to extend tool life and improve workpiece finish. These two major effects, lubrication and cooling, are best accomplished by oil-based and water-based fluids, respectively. "Cutting and Grinding Fluids: Selection and Application", p. 5, R. K. Springborn (Ed.), Am. Soc. Tool & Mfg. Engs. (Dearborn, Mich. 1967).
Finally, the contamination of machine tool lubricants, i.e., hydraulic fluids by metalworking fluids and vice-versa, can be a serious problem. If the problem of contamination is ignored, costly repair of machines will result, together with increased machine down-time and loss of production. Multi-purpose fluids have been proposed to overcome this problem. However, there does not exist, to date, a water-based hydraulic and metalworking fluid which is free of the defects of petroleum-based fluids and which can provide enhanced viscosity, lubrication, stability and wear properties required for hydraulic machinery and the like.
Urethane polymers employed in aqueous thickening compositions are disclosed in U.S. Pat. No. 4,426,485. It is said that these urethane polymers provide better thickening and leveling characteristics than do traditional cellulosic thickening agents in waterborne coatings. Such thickened compositions are stated to be useful in a wide variety of applications. However, only latex compositions are mentioned. Additionally, no reference or suggestion is made to the use of these urethane polymers in hydraulic or lubricant systems in association with the dimer esters of this invention.
The application of shear to compositions containing the above-described urethane polymers decreases their viscosity to a significantly greater extent than when these urethane polymers are used in the presence of a dimer ester of this invention.
British Pat. No. 1,069,735 also discloses the use of urethene polymers as a thickening agent for aqueous preparations. These urethane polymers are the reaction products of polyethylene glycol ethers and isocyanates. These compositions are stated to be suitable for emulsions of cutting oils. However, this patent does not disclose or suggest the use of such urethane polymers in combination with the dimer esters utilized in this invention.
Dimer esters utilized as thickeners are disclosed in U.S. Pat. No. 4,317,740. This patent discloses that water-soluble polyesters, which are the condensation product of a polyoxyalkylene glycol of a particular molecular weight and the addition product of a dimer fatty acid and maleic anhydride, are useful as lubricants and viscosity adjusting additives in aqueous hydraulic systems. This patent, however, does not disclose or suggest the use of these dimer esters in association with the instant polyurethanes.
Moreover, the application of shear to compositions containing these dimer esters decreases their viscosity to a significantly greater extent than when these dimer esters are used in the presence of a urethane polymer of this invention.
U.S. Pat. No. 4,395,351 discloses polyether-based thickeners for aqueous systems. These thickeners are mixtures of a polyether and an ethoxylated phosphate ester, or the ester and a water-soluble amine. This patent, however, does not disclose or suggest the use of these polyether-based thickeners in combination with urethane polymers to achieve the superior viscosity and shear stability characteristics of the subject invention. Furthermore, this patent teaches that the selection of suitable thickening agents is an empirical and complex task. "The diversity of available thickening agents is an indication that not all are equally useful. It is not unusual to find some thickening agents which perform well in a certain environment and not at all in another environment. In [fact], in some uses, no one thickening agent is completely satisfactory and there is a continual need and a continuing search for new thickening agents to satisfy many unmet needs." (col. 1, lines 17-24).
Various efforts to produce thickened, water-based hydraulic and metalworking fluids have been proposed. For example, U.S. Pat. No. 4,312,768 discloses the preparation of thickened, water-based hydraulic and metalworking fluids. These fluids contain a water-soluble polyoxyethylated aliphatic ester, a sulfurized metallic compound, a phosphate ester salt, and a polyether polyol thickening agent, which is further modified by reaction with a alpha-olefin epoxide. However, there is no suggestion in this patent that fluids having excellent hydraulic and metalworking properties can be provided by the utilization of polyurethanes which interact with the dimer esters of the subject invention.
Accordingly, a need exists for thickened, water-based hydraulic and metalworking fluid compositions and concentrates which maintain a high viscosity after shear stress, in addition to providing sufficient lubrication, safety, environmental compatibility and reduced cost.